1. Field of the Invention
The present invention relates to an interface (electroencephalogram interface) system which allows a device to be manipulated by utilizing an electroencephalogram. More specifically, it relates to an electroencephalogram interface system incorporating an apparatus which, in order to measure and precisely analyze an electroencephalogram of a user in real time, determines whether the user is in a state of issuing an electroencephalogram for selecting a menu item or not by utilizing a negative component of the electroencephalogram of the user while using an electroencephalogram interface, such that the negative component appears before highlighting of a menu item, and eliminates the case where no electroencephalogram for making a selection is being issued.
2. Description of the Related Art
In recent years, various types of information devices such as television sets, mobile phones, PDAs (Personal Digital Assistants) have gained prevalence and entered into people's lives. Thus, users need to manipulate information devices in many scenes of their usual lives. Usually, in realizing a device manipulation, a user utilizes a hand to input an input command via an input means (interface section) such as a button. However, in situations where both hands are full because of tasks other than a device manipulation, e.g. household chores, rearing of children, or driving, it is difficult to make an input by using an interface section and it is impossible to realize a device manipulation. Therefore, there are increasing needs of users to manipulate information devices in every kind of situation.
In answer to such needs, input means utilizing biological signals from a user has been developed. For example, Emanuel Donchin and two others, “The Mental Prosthesis: Assessing the Speed of a P300-Based Brain-Computer Interface”, IEEE TRANSACTIONS ON REHABILITATION ENGINEERING, Vol. 8, June 2000 (Hereinafter, Non-Patent Document 1) discloses a electroencephalogram interface that utilizes an event-related potential of an electroencephalogram for distinguishing an option which a user wishes to select. To specifically describe the technique described in Non-Patent Document 1, options are randomly highlighted, and a P3 component of an event-related potential which appears about 300 ms after a point in time that an option was highlighted is utilized to enable distinction of the option which the user wishes to select. According to this technique, a user is able to identify an option which he or she wishes to select, without using a hand.
As used herein, an “event-related potential” refers to a transient potential fluctuation in the brain which occurs in temporal relationship with an external or internal event. An electroencephalogram interface utilizes an event-related potential which is obtained from a stimulation to the visual sense as an external event. For example, within the event-related potential for a visual stimulation, a so-called P3 component may be utilized to perform processing such as switching of channels, selection of a program genre of which viewing is desired, and sound volume level adjustment. The “P3 component” refers to a positive component of the event-related potential which appears in a time slot of 250 ms to 500 ms after a target stimulation is presented, regardless of the type of sensory stimulation such as auditory sense, visual sense, or somatic sensation.
For an application of the event-related potential to an interface, it is important to distinguish the event-related potential (e.g., the P3 component) of a subject with a high accuracy. Therefore, it is necessary to accurately measure a biological signal and accurately distinguish the measured biological signal with an appropriate distinction technique.
There are generally two causes of a lowered distinction ratio. A first cause is that, although being contained in an electroencephalogram, a component (e.g., the P3 component) which is used for an electroencephalogram interface has a low S/N, and results in a low accuracy of the distinction technique. This makes it difficult to perform a highly accurate distinction, and thus the distinction ratio becomes lower. A second cause is that, depending on the state of the test subject, for example, a relevant electroencephalogram component may not have appeared in the first place, thus making it impossible to perform distinction. Since the electroencephalogram interface will try to perform distinction anyway, the electroencephalogram interface will output an incorrect result of distinction. This lowers the distinction ratio.
Regarding the first cause mentioned above, a method for removing the noise mixed in the electroencephalogram and a highly accurate distinction method are both being under development. For example, Pamphlet of International Laid-Open No. 2005/001677 discloses a technique of improving the distinction ratio which uses a band-pass filter to remove, among the noises contained in the electroencephalogram, noises that are mixed at a frequency different from the frequency of a subject of distinction (event-related potential), e.g., noises on commercial power, and thereafter performs distinction. Japanese Laid-Open Patent Publication No. 10-146323 discloses, as a technique of removing noises from living organisms which are difficult to remove with a simple frequency filter, e.g., electro-oculographic potential, a technique of excluding any samples containing an electro-oculographic potential from the subject of distinction, thus obtaining an improved distinction ratio.
Regarding the second cause mentioned above, a technique of excluding any environment which will not allow a relevant electroencephalogram component to appear has been adopted. Specifically, conventional experiments under laboratory room conditions have adopted a technique of controlling the state of a test subject by instructing the test subject to concentrate on a task in a laboratory room which is free of disturbances, or causing the test subject to press a confirmation button, etc., thus allowing a response to steadily appear.
However, when an electroencephalogram interface is used for the manipulation of an actual device that is used on daily basis, e.g., a television set or a DVD recorder, it may not always be the case that the user is concentrating on a screen indication. In other words, an electroencephalogram for making a menu selection may not always appear in the electroencephalogram of the user.
For example, even when a screen of an electroencephalogram interface is being presented, the user may be concurrently performing another task (e.g., household chores or rearing of children), thus resulting in a situation where the user is not looking at the menu but is absorbed in that task. In such a situation, it is difficult to be always gazing at the interface screen. Moreover, if highlighting of a menu item begins while the user is in the process of selecting a menu item to choose next, it results in a situation where no electroencephalogram for making a menu selection is present. The user needs time to select a menu item to choose next. Therefore, it is difficult to assume that an electroencephalogram for making a selection will appear immediately after an electroencephalogram interface menu is presented.
The aforementioned example corresponds to the second cause mentioned above, i.e., a situation where a relevant electroencephalogram component has not appeared in the first place. Since many such situations are conceivable, it is presumable that there will be increasing situations where it is impossible to make an electroencephalogram-based distinction.
Now, when the user is not looking at the menu items, a P3 component will not appear even if a menu item which the user wishes to select is highlighted. However, if a noise of a waveform resembling the P3 component is accidentally mixed, for example, a menu item which is not intended by the user will be selected. This is a problem which is unexpected from any experimentation under laboratory-room conditions, and was first recognized in connection with measuring an electroencephalogram on daily basis for use in an interface.